Which law of chemical combination?

1.08 gram of \(\ce{Cu}\) wire was allowed to react with nitric acid. The resulting solution was dried and ignited
when 1.35 gram of copper oxide was obtained. In another experiment 2.3 gram of copper oxide was
heated in presence of Hydrogen yielding 1.84 gram of copper.The above data is in accordance with the law of \(\text{__________} \).